Cardiac electrophysiologic measurements may provide useful diagnostic information. As one example, ventricular repolarization may be an indicator of arrhythmogenic risk. Ventricular repolarization may be visualized clinically in the electrocardiographic T wave, but T wave morphology is highly volatile because it is influenced by factors such as heart rate, autonomic nerve tone, pharmacological interventions, and electrolyte imbalances. Factors such as slow conduction, conduction block, spatially heterogeneous repolarization, and rate dependent changes in both conduction and repolarization may also contribute to complex electrophysiologic conditions that may increase the chances of life threatening cardiac arrhythmias.
To assess repolarization change, the QT interval, the time between the onset of the ECG (electrocardiogram) QRS complex and the end of the ECG T wave may be measured. Measurement of the QT interval may entail a number of difficulties, however. For example, T offset occurs during a low signal-to-noise (SNR) portion of the ECG, and may depend upon the leads in which the QT interval is measured as well as upon the activation sequence.
Accordingly, there is a need for more reliable systems and methods for assessing cardiac electrophysiologic phenomena such as ventricular repolarization.